This invention relates to a high pressure valve assembly useful for taking streams of fluids at relatively low pressures and transferring them to high pressure streams. Such valves experience great wear when the fluids involved are solids-containing slurries, such as, for example, steamed wood chips in liquor, as is known in the pulp and paper industry.
It is generally known in the industry employing such high pressure rotary plug valves having offset ports in the rotary plug that the solids in the slurries so handled tend to cause wear in the valve plug and surrounding liner in circular bands at the top, central portion and bottom of the rotary plug and corresponding portions of the liner. This wear pattern can be overcome temporarily by laterally adjusting the plug in the valve housing until the wear becomes too great, i.e., the plug impinges on the end bell or cover or until lateral displacement causes undesired overlap of the offset ports allowing the slurry to leak back from the high pressure side to the low pressure side.
In an effort to reduce valve body wear, pressure equalization and purge lines have been added directly to the high pressure feeder with the point of tie-in at the end bells. Thus, a continuous purge is provided to keep the end bells free of fine solids contained in the slurry, causing wear at each end of the valve. This results in an equalization of pressure on the ends of the valve and decreases the load on the valve with a resultant increase in valve life and decrease in operating cost.
However, end bell purging has no effect on the circular banding wear which occurs on the valve plug and liner. Such wear patterns require rebuilding the valve after a relatively short service life, i.e., from at least 6 months to not more than 3 years with an average service life of about 15 months. Thus, there is a need for improved life high pressure rotary plug valves. There is also a need for such valves having decreased circular banding wear, decreased operating load and increased service life. These and other additional needs are met by the article of the present invention.